Plant form and function is ruled by cells


  • Plant cells range from 10-100um in length


  • Cell walls maintain physical framework
    • maintain cell turgidity


  • Root cells start uptake & transport of H_2_O
  • Leaf cells are specialized for photosynthesis


  • Cells of flowers control reproduction
    • produce pigments and nectar

Plant cell walls



  • Mostly made of cellulose
    • strength and protection of protoplast
    • chains of cellulose molecules = fibrils


  • Metabolism does occur (not inert)


  • Consists or 1 or 2 layers
    • primary wall (1st layer) = cellulse fibers
    • secondary wall (internal) = lignin


  • Sticky layer (lamella) between walls
    • made of pectin (jelly!)

Support or water conducting cells have secondary walls


Cellulose and lignin extremely abudant on Earth


Why dont plants have strong bones made of Calcium?



  • Animals with shells use calcium carbonate
    • carbonate comes from seawater, so pH not affected


  • Animals with internal skeleton use calcium phosphate
    • cant handle carbonate
    • phosphate has little effect on cell acidity


  • Plants must also be careful with Calcium and its salts
    • plants need phosphate badly
    • lignin and cellulose are inert
    • lignin and cellulose carbs from photosynthesis

Plant cells are not solid structures (cytoplasm channels)


Plant cells are not quite individuals





  • Plasmodesmata diminish individuality of cells
    • symplast: interconnections of protoplasm
    • living region, transport & communication


  • Cell walls do separate cells, just not cleanly
    • lots of intercellular air spaces (@ corners)
    • apoplast: cells walls + intercellular spaces
    • gas diffusion occurs via apoplast
    • water through cell wall via capillary action

Plant cell membrane structure fits fluid mosaic model






  • Membrane covers the surface of the protoplasm
    • Molecular pumps transport molecules in and out


  • Impermeable to bad stuff, permeable to beneficial stuff

Anatomy of a plant cell



  • Virtually all plant cells, although diverse, have conserved organelles
    • roots, wood, barks, leaves, flowers
    • certain organelles can become modified


  • Contain protoplasm: water + proteins, lipids & nucleic acids


  • Nucleus, ribsomes and endoplasmic reticulum


  • Golgi apparatus: transport, modify, and package proteins & lipids for delivery


  • Peroxisomes: organelle that produces or uses peroxide
    • detoxify product of photosynthesis

Plastids: membrane bound organelles in plants & algae





  • Choloroplast: double membrane organelles in leaf cells
    • key for photosynthesis
    • interesting evolutionary history


  • Leucoplast: colorless organelles storing starch


  • Chromoplasts: organelles containing pigments for colored plant parts

Central vacuole makes up most volume in mature cells


New cells orginate from meristems



  • All plants are multicellular with active regions of cell division
    • cells mostly divide my mitosis
    • meiosis in parts of reproductive cycle


  • Growth is localized in the active regions: meristems
    • meristem cells are undifferentiated


  • Apical meristems: @ tips of roots and stems
    • cell division propels tissues ‘out’
    • primary growth of leaves, stem & roots

New cells orginate from meristems



  • All plants are multicellular with active regions of cell division
    • cells mostly divide my mitosis
    • meiosis in parts of reproductive cycle


  • Growth is localized in the active regions: meristems
    • meristem cells are undifferentiated


  • Lateral meristems: secondary growth
    • cell division adds diameter
    • support, xylem, phleom cells
    • tissues called ‘cambium’

Cancerous growth in plants?




  • Release of cell cycle arrest in humans can be fatal
    • cigarette smoke can cause lung cancer
    • UV triggers skin cancer


  • Galls: abnormal growth causes by reaction to insects/microbes


  • Irregular cell growth in plants not a big deal
    • cells cannot migrate in plants
    • no single plant organ is indispensable